1. Field of the Invention
The present invention relates to conjugated diene butyl rubber containing conjugated unsaturation in the linear backbone, and a process of preparing same.
2. Description of the Prior Art
The expression "butyl rubber" is used in the rubber industry to describe copolymers made from a polymerization reaction mixture having therein from 70 to 99.5% by weight of an isoolefin which has about 4 to 7 carbon atoms, e.g., isobutylene, and about 30 to 0.5% by weight of a conjugated multiolefin having from about 4 to 14 carbon atoms, e.g., isoprene. The resulting copolymers contain 85 to 99.5% by weight of combined isoolefin and about 0.5 to 15% of combined multiolefin. The preparation of butyl rubber is described in U.S. Pat. 2,356,128 which is incorporated herein by reference.
The polymer backbone of commercial butyl rubber is made up primarily of isobutylene units, with just a few percent of isoprene units. The isoprene units contribute the small amount of unsaturation present in butyl rubber. The basic preparative equation is represented by: ##EQU2## WHICH COMBINE IN THE PRESENCE OF Friedel-Crafts catalysts to form: ##EQU3## where n + l represent the number of isoolefin units incorporated in the butyl rubber, while m represents the number of initial diolefin units present, substantially as isolated units. The conjugated diolefin, isoprene, loses one olefinic linkage upon its essentially random incorporation into the polymer backbone.
Thus, butyl rubber, as presently produced, contains only a small percentage of unsaturation, in the form of the single double bond associated with the isoprene residue which is incorporated more or less randomly throughout the polymer chain.
Halogenated butyl rubber has been developed in recent years and has contributed significantly to the elastomer business. A method of preparing halogenated butyl rubber is described in U.S. Pat. 3,099,644, which is incorporated herein by reference. Both chlorinated and brominated butyl rubber are well known in the art. The formula for halogenated butyl rubber is typified by: ##EQU4## where n, l and m have the same values as for butyl rubber, described above, though this structure is but one of several which can be formed, depending on the conditions of halogenation, the halogenating agent used, etc.